1. Field of the Invention
The present invention relates to a black toner used for an electrophotography method, an electrostatic printing method, a toner jet method, or the like.
2. Description of the Related Art
Up to now, many problems occur when using carbon black as a coloring agent for the production of toner.
First, carbon black has a small primary particle diameter and a large specific surface area as compared with other pigments. Therefore, carbon black is hardly dispersed or is unevenly distributed on the surface of a toner particle. Further, free carbon black is easily produced. Because carbon black is fine particle having a high adhesiveness, presence of free carbon black causes deterioration of flowability of toner and prevents satisfactory triboelectric charging, and particularly tends to deteriorate reproducibility of a half-tone image. Moreover, in the case where carbon black is not sufficiently dispersed, a problem also arises in that a sufficient image density is not obtained.
Secondly, charges of toner easily leak when the carbon black is present on the surface of toner because the carbon black has conductivity. Therefore, when forming image by using such toner, fogging, toner scattering, or transfer skip occurs.
JP 64-35457 A and JP 01-145664 A are applications relating to improvement of dispersibility of carbon black. However, it cannot be said yet that the problems concerning dispersibility are completely solved.
Moreover, JP 07-64337 A and JP 10-186713 A disclose the improvement of dispersibility of carbon black and charging property of toner by combining carbon black having specific physical property and an azo-based iron compound having a specific structure. For example, the method disclosed in JP 10-186713 A is a superior method of obtaining toner having high coloring property and stable charging property but it has a few problems on solid image uniformity and durability under a high-humidity environment.
Furthermore, since an awareness regarding a global environmental issue is growing up, there arises a tendency of using all resources effectively. As for the toner, several attempts have been made. One of such attempts is “a reduction of waste toner”. The waste toner is one which is not successfully transferred to a transfer material such as paper after developed on a photosensitive drum, and it should be reduced in every way in view of effective use of resources. Methods of improving transferring property by using external additives so as to reduce the waste toner are described in, for example, JP 49-042354 A, JP 55-026518 A, JP 58-060754 A and JP 61-277964 A. However, in order to further reduce the waste toner, it has been eagerly demanded to more finely disperse carbon black in a toner particle so as to improve the transferring property.